Former Yahoo executive says up to 3bn user accounts may have been stolen by hackers

The number of accounts is much higher than the 500m being reported, according to source.

Yahoo has not disclosed the full extend of the data breachJustin Sullivan/Getty Images

A former Yahoo executive has said that up to three billion user accounts may have been compromised in 2014's security breach, considerably larger than the 500 million estimated by Yahoo.

The source, alleged to be "a former Yahoo insider familiar with the company's security practises", has revealed because of the way its user information is stored, the breach would have exposed a far greater quantity of account information.

However the former executive, who is allegedly in contact with Yahoo employees investigating the breach, told Business Insider: "I believe it to be bigger than what's being reported. How they came up with 500 (million) is a mystery". They instead claimed it may be anywhere between one and three billion.

All customers notified

It is currently unclear whether the breach was a state-sponsored attack or carried out by criminals, with Yahoo and cybersecurity firms currently at odds over who is to blame.

A Yahoo spokesperson told IBTimes UK that the company had notified all of the users thought to have been affected by the breach, adding: "Based on the ongoing investigation, Yahoo believes that information associated with at least 500 million user accounts was stolen...We stand by these numbers and note this is an ongoing investigation."